The life story of a jellyfish.

News and commentary about environmental issues.
Aug. 29 2008 4:15 PM

The Life of a Jellyfish

From a continuing series on revolting creatures.

Illustration by Alex Eben Meyer. Click image to expand.

A really good place to have a meaningful and pain-free relationship with jellyfish is the Monterey Bay Aquarium. Behind glass, artfully illuminated, the creatures are the very definition of elegance—beautiful in movement and appearance. People stand quietly, mesmerized, watching the translucent bells pulse at a hypnotic 30 beats per minute, a little slower than Lance Armstrong's heart rate.

Encounters without a glass wall—dangling tentacle to defenseless skin—are not so happy. August is the month. (January if you're Aussie.) Don't worry, there's still time: You might just as well get stung over Labor Day weekend.

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A profusion of jellyfish is often described as an invasion or an attack. Which is laughable, given the guiding principle of jellyfish behavior—"whatever." No brain, no spine; they don't have the capacity to plan a beach invasion. We bump into them, and because we're too big to eat, they perceive us as attackers.

Planning is not their forte. In place of a brain, jellies have a nerve net. Jellyfish are the free-floating relatives of sea anemones and corals, much older than fish, and not much changed for more than 600 million years. They ruled the ocean, in their passive way, when there was almost nothing but ocean. Now they drift into their food or their food drifts into them. The pulsing creates a current that pulls prey within reach.

Depending on the kind of jellyfish, its sting can be minor, memorable, or, in very rare cases, fatal. (More than 1,000 species of jellyfish have been described. Like trees in the Amazon rainforest, there are probably thousands more still undiscovered.) The stinging cells—called nematocysts—are embedded in the tentacles and the umbrella of the jellyfish. The nematocyst generates a dart; the dart gets fired into prey, delivering a cocktail of neurotoxins, and then falls off the jellyfish. The nematocyst then goes to work generating a new dart for the next victim. Sometimes a tentacle or glob of jelly mucus breaks off and the slimy transparent stuff sticks to human skin, which is, to put it mildly, disconcerting.

Enough about our feelings: What's it like to be a jellyfish? Is it boring to be a drifter? "All the medusa has to do," says Monty Graham, marine scientist at the Dauphin Island Sea Lab in Alabama and convener of the first International Conference on Jellyfish Blooms, "is eat and have sex. I don't call that a bad life." (The floating stage of the jelly, with its dangling tentacles, is named for the snake-haired monster.)

It's not well understood how the jellies find each other for mating. "Don't think of jellyfish trying to seek each other out," Graham said. "Think of it in terms of avoiding being carried away from each other." Staying close to potential partners involves the following three talents: They have the ability to sense light and dark, though they have no eyes. They perceive gravity and can tell up from down. They can position themselves in relation to currents. Once they've sensed the right placement, the males release sperm from their mouths into the ocean and hope for the best—another whatever/wherever behavior. The odds are good because males and females are in a swarm; clouds of sperm and eggs swirl in the water. The moon jellyfish, the pretty pearly one common along our coasts, is a little more focused. The male sends his sperm out in a long string—the length of a strand of spaghetti. The female catches it and eats it. Happily for the survival of the moon-jelly race, her mouth is the route to her eggs.

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